He goes to work by solar bike!

I had met him in Pau last summer, he had come to meet the participants of the Sun Trip France 2020 and to see their solar bikes. He was very enthusiastic about this mode of transport, and we had a good chat!

Grégory has made his project a reality: since last fall, he has been traveling by solar bike to the various places where he leads workshops for young audiences. 2000 km traveled to date! This approach is fully consistent with the purpose of its activities: discovery of nature, scientific, sensitive or artistic approach, preservation of the environment … (Find out more on Terra Pitchoun )

Grégory found good listening with Déclic Éco who designed and built the bike perfectly suited to his professional needs.

The Sun Trip achieves its objective: to spread the concept of solar bike!

The evolution of my solar bike from 2017 to 2021

From my first participation in the Sun Trip in 2017 until today, I have experimented with different configurations of solar bikes.
Here are the basic principles that guided my constructions:
– from 2017 to 2019, I wanted to be able to take my vehicle by train. So I opted for a classic bike associated with a single-wheel trailer carrying the solar panels (which could tilt vertically).
– for the Sun Trip 2020 which was to take us to China, my goal was to be able to have as much solar energy as possible. So I associated my solar trailer (3 panels) with a recumbent bike on which I added a solar roof (2 panels). Thus, I reached the maximum solar surface accepted on the Sun Trip (almost 2.5 m² which corresponds to a power of 500Wp). In 2021, I transformed the trailer a bit.

2017Extrawheel modifiée200WcBionX
200Wc +100Wc à l'arrêtCrystalyte SAW (roue avant vélo)
300 WcCrystalyte SAW (roue remorque)
300 Wc9Continent RH205 (roue arrière vélo)
500 Wc9Continent FH212 (roue avant vélo)
500 Wc9Continent FH212 (roue avant vélo)

Preparation of the Sun Trip Europe in April

Obviously, this month of April will have been marked by the re-containment and the limit of 10 km around the home! Luckily, half of my perimeter was surrounded by nature and was quite hilly. It was also the opportunity to discover or rediscover side roads and small forgotten roads … I saw spring unfold visibly, despite an episode of snow and night frost.

By knitting in this perimeter, I increased the distance covered each week. For my longest outing, I managed to do a 200 km lap with 2600m of vertical drop!
April ends with rain! Suddenly, the bike remains in the garage and I take this opportunity to refine the itinerary for this summer and publish a few articles.

Date GPS Dist.
h : mn
27/04 164 5:42 28,9 2355 1902
24/04 203 6:49 29,7 2732 2327
23/04 104 3:38 28,6 1372 1178
15/04 81 3:06 26,1 1175 633
10/04 71 2:48 25,4 825 159
08/04 52 2:00 27,9 670 171
02-04 232 8:40 26,8 2545 2010
Avril 908 32:19 28,1 11674 8380

April 2: 3rd Sun Trip Europe preparation outing

It was the 3rd great preparation outing for the Sun Trip Europe before the reconfinement.
I was able to enjoy the beautiful landscapes of Côte-d’Or, visit corners that were unknown to me. And I even drove a bit in Saône-et-Loire. It was good to ride in the sun, without fear of miles.
To say that the confinement will soon lock us into a 10km perimeter around our home!
Tour: 232 km
Elevation +: 1590m
Consumption: 2540 Wh
Production: 2010 Wh

March 31: 2nd Sun Trip Europe preparation outing

The first outing being conclusive, I wanted to continue my momentum and exceed 200 km during the day. The sun was 100% with me, but the solar power is obviously less in March than in summer (between 60% and 70%). I wanted to see the amount of energy produced by the panels under these conditions.
Consumption: 2130 Wh
Production: 1720 Wh

Installing solar panels on a bike

Installing signs on a bicycle raises many problems. The solutions are many and varied, as we can see during the various Sun Trips.
The designer is led to make choices, according to his priorities, his taste and his budget.
Most often, priority is given to a type of bike (classic, recumbent, cargo bike, trike …) the solar equipment will then have to adapt to it.

But sometimes, other constraints are chosen as priorities and guide the design:
– have a large solar surface, to capture a maximum of energy,
– have a large capacity battery, to store more energy in poor weather,
– design a very light vehicle to easily climb the mountains,
– design a very solid vehicle, to avoid breakage during long journeys,
– have a foldable vehicle easily for transport.

We dream of the ideal vehicle, light, solid, powerful, with a long range. Very quickly, you realize that all these wishes conflict with each other. Increasing the surface area of ​​the panels and the supporting structure contributes to weighing down the vehicle. Likewise, with increasing battery capacity. Lightening the vehicle as much as possible can make it too fragile to face the road and vibrations.

Since 2017, I wanted to have a vehicle that can be taken by train: I opted for a classic bike and a folding single-wheel trailer. In 2018, I tested a folding bike with a foldable trailer to be able to take the vehicle on international buses. The maximum area of ​​panels that I managed to install on a trailer was 1.5m², corresponding to a power of 300Wp.

I have not explored the possibility of installing panels on the bike, on the roof, as did Daniel Jeni during the Sun Trip 2018. Maybe I would try this idea one day?

Preparation of the Sun Trip 2020 Lyon-Canton

I wanted to have the maximum authorized solar surface, 2.5m². For this I first considered using a cargo bike and then a tandem.
Finally, it was thanks to Guillaume Devot of Déclic Eco that the idea of ​​using a recumbent bike came to life. Installing 1m² of panels on the bike completes the 1.5m² of trailer panels.
But a concern remained: would this configuration be easy to drive on the road, even in the case of a strong side wind? Experience has shown me that it is.

It remains for me to test the efficiency and solidity of the supporting structure of the panels on the bike.
The trailer structure has proven itself in 2018 and 2019 over 6000 km. It’s reassuring because I could observe that the vibrations and shocks of the road, over thousands of kilometers, really test the load-bearing structure of the panels.

For learn more about choices adopted by other participants in the various Sun Trips

D-5 before the Sun Trip France!

In the last issue of Télérama magazine, the article entitled “Happy traveling differently” offers the reader to “give character” to his vacation by visiting Bourgogne-Franche Comté.
For my last test trips, I followed this advice with a tour of Southern Burgundy. Because testing your solar bike does not prevent you from discovering the heritage and the landscapes!
The excellent sunshine of yesterday allowed me to cover 207 km in just over 6 hours.

July 8:

July 7:

Training with the Solarduino Bike 2020 solar bike

Two months is the time, from May 11 (deconfinement) to July 11, to test and test my new solar vehicle. You have to work hard!
The challenge # 1: taming the recumbent bike, for me it’s brand new! Know its road behavior with the solar roof, with the trailer, in turns, potholes, in gusts of wind.
I also have to test the mechanical part, in particular the supports of the solar panels on the bike as on the trailer.
Finally, I need to know my new engine, its performance, its consumption …
A beautiful program!

Voir en plein écran

Date GPS Dist.
H : mn
08-07 207 1290 06:11 33,5 1536 2456 4,1
07-07 103 800 03:08 32,9 707 1264 2,3
01-07 82 965 03:00 27,3 592 985 8,7
30-06 132 1245 4:15 31 881 955
27-06 55 768 1:55 28,5 370 424
26-06 72 430 2:19 31,1 465 441
23-06 157 1395 5:15 29,8 1085 2171
20-06 63 170 1:44 36,3 420 76
19-06 29 130 0:51 33,4 208 52
17-06 108 617 3:21 32,1 713 443
16-06 65 570 2:04 31,1 461 287
15-06 72 590 3:20 25,2
24-05 111 710 4:20 25,4
21-05 93 705 4:25 21
H : mn

Anatomy and weight of my Solarduino Bike 2020 solar bike

VéloVélo Nazca Pioneer, pneus Schwalbe
Marathon Plus Tour,
moyeu Rohloff
25,5 kg
Moteur Nine Continent FH2126,0 kg
Contrôleur0,3 kg
Batterie5,5 kg
Panneaux (2)1,6 kg x 2
Cornière alu,
tube horizontal,
supports verticaux
0,9 kg x 2
0,9 kg x 1
Régulateurs solaires0,29 kg x 1
0,46 kg x 1
Câblages0,30 kg
RemorqueTimon Bob Yak1,30 kg20,8 kg
Structure remorque5,00 kg
Roue1,35 kg
Planche bagage0,55 kg
Panneaux solaires1,50 kg x 3
Cornières alu, traverses bois,
tube carbone kevlar
4,15 kg
Régulateur solaire (1)0,29 kg x 1
Régulateurs solaires (2)0,46 kg x 2
Système d'inclinaison0,80 kg
Câblage0,30 kg
et bagages
12,5 kg
Total58,8 kg

Build your solar bike
Part 3: solar equipment

Table of contents
Part 1 : the bike
Part 2 : the electric assistance
Part 3 : the solar equipment

Solar panels cannot be connected directly to the battery, they must be connected through a solar regulator.

3.1. Solar regulator

This is responsible for adjusting the voltage to that of the battery (36 or 48 Volts for example) and modifying the current (Amps) according to the amount of light energy supplied by the sun.
The most common type among solar cyclists is the MPPT “boost” technology regulator.
The regulator’s MPPT technology ensures the best possible efficiency in the conversion of electrical energy. The qualification “boost” means that the voltage of the panels at the input of the regulator must be lower than that of the battery and the regulator then adjusts the output voltage to that of the battery.

3.2. Solar panels

The preferred panels are flexible monocrystalline silicon panels: they are light and have a good conversion efficiency of light energy into electrical energy. Better to forget the models developed for the roofs of houses, in polycrystalline silicon (very heavy, lower performance).

Article: how to choose your solar panels

The solar bike builder will have to choose the format of his panels according to his bike and the structure planned to support them.
To participate in the Sun Trip, the width of the panels must not exceed 1 meter which corresponds to 7 photovoltaic cells (in the costing dimensions of 12.5cm x 12.5cm). But the traditional formats have rather even numbers of cells, in practice, a majority of solar cyclists now have panels of 6 cells in width.

2 cells =28cm 4 cells =54cm 6 cells =80cm

The length of the panels will depend on the bike chosen, or the trailer …
Warning: the size of the panel has a direct influence on its electrical characteristics, it is advisable to ensure the adequacy between panels, regulators and battery.

The quality of a panel, in terms of electricity production, depends a lot on the quality of the photovoltaic cells that constitute it. In the technical sheet, the mention of a major cell manufacturer is a guarantee of quality.
However, the big manufacturers sort their cells and sell them in different quality grades. But this clue is never mentioned by the panel manufacturer.

Article: the performance of a photovoltaic cell

Article : comparative performance test of 3 solar panels

3.3. Support structure for solar panels

How to transport solar panels on a bicycle? This is one of the important questions that the solar cyclist asks himself. This question is also related to the surface of panels that one wishes to install.
If installing 1 panel of 0.7 m² is quite simple, installing 2.5 m² of panels is much more complicated.

Article: install solar panels! Yes but how?

Article: the installation of panels solar on my bikes

Building your solar bike
Part 2: electric assistance

Table of contents
Part 1 : the bike
Part 2 : the electric assistance
Part 3 : the solar equipment

The electrical assistance system includes at least a battery, a motor, a motor controller (sometimes integrated inside the motor), a control and display console. Other elements can be added: pedaling sensor, torque sensor, speed sensor, handlebar accelerator …

2.1. The battery

As explained in Part 1, the batteries supplied with some commercial bicycles cannot be charged during use, which greatly complicates their integration into a solar bicycle.

Battery specifications
The main characteristics of a battery are:
– chemical technology: today, most bicycle batteries use Litium-Ion technology.
– the nominal voltage: 36 Volts, 48 ​​Volts, or even 52 Volts,
– the capacity, expressed in Ampere-hours or in Watts-hours. This value reflects the amount of energy that the battery is able to store and restore.

Components of the battery
A battery is made up of a set of Li-Ion elements (called “cells”) associated in series and in parallel, to which an electronic protection system (BMS) is added. The role of the BMS is to prevent too deep a charge or discharge and to balance the voltages between the Li-Ion cells.
Most batteries are made up of cells called “18650”, with reference to their physical format (diameter = 18mm, length = 65mm).

Association of cells in series
The nominal voltage of an 18650 cell is 3.6 Volts.
To make a 36 volt battery, we put 10 cells in series.

 For a 48 battery Volts, the series has 13 cells.

Association of cells in parallel
Manufacturers offer 18650 cells in different capacities: 2000, 2500, 2900, up to 3500 Milliampere-hour.
In the example shown below, we have chosen 3500 mAh cells. The set includes only 1 series, its overall capacity is 3500 mAh or 3.5 A-h.

In the second example shown below, still with 3500 mAh cells, 4 series of 10 cells have been associated in parallel. The resulting battery has an overall capacity of 14 A-h.

High capacity cells (3500 mA-h) are often the most expensive, but their advantage is that they can store more energy at equal weight. In other words, at equal capacity, the battery will be lighter, which is an advantage for the solar cyclist.
As for the quality of the cells (capacity, longevity), it is often better among large manufacturers such as LG, Samsung, Sanyo …

2.2. The engine

There are different types of engines, each with advantages and disadvantages. Knowing them will be an asset in making the best choice according to the intended use.

2.2.a. The Direct Drive “wheel” motor

It is inserted into a wheel instead of the hub, this Direct Drive type has no gears inside. There are models for front wheel or rear wheel. Front wheel models can optionally be installed on a trailer.
Benefits: very reliable, no maintenance. On descents, the motor can brake and regenerate electricity to recharge the battery.
Disadvantages: heavier than the reduced motor, and less efficient on very steep hills where it gets hot.

2.2.b. The reduced “wheel” motor

It is inserted into a wheel instead of the hub, it has gears inside. There are models for front wheel or rear wheel. Front wheel models can optionally be installed on a trailer.
Benefits: smaller engine, less heavy, often more efficient than Direct Drive on hills. . It does not brake the bike when pedaling without assistance.
Disadvantages: Gears to be regularly maintained and changed after long distance trips. No regeneration on descents.

2.2.c. The “pedal” motor

This motor is inserted in place of the original crankset, it has gears inside.
Benefits: smaller engine, less heavy, very efficient on hills. It does not brake the bike when pedaling without assistance.
Disadvantages: Gears to be regularly maintained and changed after long distance trips. No regeneration on descents.

2.3. The motor controller

Depending on the system, the controller can be independent or integrated into the engine block. It is very often independent in wheel motor systems and often integrated into pedal motors. Its role is to manage the energy supplied to the motor, as a function of several data (level of assistance chosen, speed, energy available in the battery, signal from the torque or pedaling sensor, etc.).

2.4. The control and display console

It gives indications to the user (eg: speed, level of assistance, battery voltage, distance traveled, etc.) and, moreover, it allows him to communicate with the system (at least to choose the level of assistance).

In advanced systems, such as those manufactured by the company Grin Technologie, the Cycle-Analyst console, allows the display and selection of a very large number of parameters: speed, power consumed, assistance levels, etc. additional equipment allows simultaneous display of solar production. It is thus possible to know in real time the amount of energy consumed and produced.

In the photo above, we can see that the consumption by the motor is 353W at this precise moment, while the solar production is 371W.

2.5. The pedaling sensor or the torque sensor

Depending on the system, this sensor may be separate or integrated into the engine block, in which case it is not visible. The most advanced systems have a torque sensor that measures the power given by the cyclist, the others a pedaling sensor that measures the cyclist’s pedaling pace.

2.6. The speed sensor

Depending on the system, this sensor can be separate or integrated into the engine block.

2.7. The handlebar accelerator

It is an optional accessory. It is authorized in France only for starting, for example after a red light. It is often very useful, especially on recumbent bikes, for hill starts.

Building your solar bike
Part 1: the bike

A solar bicycle is made up of the following components: a bicycle, sometimes combined with a trailer, an electric assistance system, and solar equipment.
We will describe these elements below, and consider the different possibilities available to those who want to build their solar bike.

Table of contents
Part 1 : the bike
Part 2 : the electric assistance
Part 3 : the solar equipment

1. The bike

It is possible to use either to use a commercial electric-assisted bicycle, or to use a conventional bicycle to which an electrification kit is added.

1.1 A commercially available electrically assisted bicycle

In this case, be aware that many major manufacturers prevent the user from recharging the battery while the engine is running. This then requires having 2 batteries: one is recharged by the solar panel while the other supplies the motor, which means that the batteries must be replaced periodically. We understand that this system is not the most practical.
In addition, some manufacturers even prevent charging the battery other than by connecting it to the mains charger, which further complicates the task.
But some rarer commercial bikes do not have these limitations and can be easily converted into solar bikes.

1.2 A simple bike to which we add electric assistance

On reading paragraph 1.1, we understand that it is often easier and more efficient to install an electric assistance system on a non-electric bicycle.
Two ways to proceed:
– either by purchasing a complete kit (advantages: simplicity / disadvantages: if the system is “proprietary”, the user cannot use parts from another brand),
– either by composing a kit, by choosing each element (advantages: the choice of each element is much wider, you can better adjust the elements to your own needs, to your practice / disadvantages: the range of possibilities can confuse the beginner).

To read: note from the Directorate of Legal and Administrative Information (Prime Minister): https://www.service-public.fr/particuliers/actualites/A14325

1.3 Different types of bikes possible

The choice of the bicycle is important because it will often condition the way of installing the solar panels, on the bicycle itself and / or on a trailer.
Many types of bikes have been tried out, according to individual tastes:

  • classic upright bike with trailer, 1 or 2 wheels,
  • classic upright bike with solar roof,
  • straight-lying tandem transformed,
  • cargo bike, with panels on the bike or on the roof,
  • recumbent bicycle with panels on the roof, and sometimes in tow,
  • trike, tandem trike, with panels on the roof, and sometimes in tow,
  • velomobile with panels on the roof, and sometimes in tow.

See the different types of bikes on the Sun Trips since 2013.

Crossing a Chinese desert, on foot and in solar mode!

I discover this amazing video made by Olivier Coste. He designed a solar powered machine to carry his equipment in a desert environment: “Solar Explorer”. In 2018, he crossed the Badain Jaran Desert in China. His vehicle allowed him to tackle the highest dunes in the world loaded with more than 150 kilos of equipment, water and food. Without such a carrying system, these arid areas would be inaccessible to a single individual. Congratulations to Olivier for this innovation!

Sun Trip 2020 preparation seminar

Preparation for the Sun Trip 2020 was organized this weekend in Lyon. It brought together 30 participants from the fifty or so registered participants and took place in an atmosphere that was studious, fascinating and friendly.
To effectively prepare for this solar bike rally, many themes were addressed:
– administrative aspects, border formalities and visas,
– possible routes and variants,
– the cultural differences of the countries crossed,
– the operation of solar bikes, the technical regulations,
– monitoring of meteorology and its impact on navigation,
– communication: video, social networks etc …

This weekend also allowed everyone to meet the other participants. There were many informal exchanges, between conferences and workshops, around meals or over a beer, at all hours of the day and night!
It was an opportunity for rich meetings between experienced suntripers and newcomers, between French and English speakers, between technicians and travelers … The enthusiasm and the joy of sharing were visible on the faces.

Saturday evening, we celebrated the Chinese New Year in the presence of the Chinese Consul in Lyon and the 3 Chinese SunTrip managers. On Sunday, Luc Giros presented his tour of Europe: more than 18,000 km traveled on the solar bike used by Mickaël Joguet during the Sun Trip 2018.

We would like to thank Florian Bailly for organizing this fruitful moment, as well as all the members of the organization who contributed to the smooth running of the event: Béatrice and Yannick, Christophe Bayard (Vécolo), Benoit Ganivet, Annick-Marie who brilliantly provided case-simultaneous translation for non-French speaking participants.

To take the train with a solar bike !

The after Sun Trip Tour: from Valence to Dijon via Châlon-sur-Saône

On July 20th, I leave Valence in TER to join Châlon-sur-Saône. I use the idea that guided the design of my solar vehicle: to take the train. Principles: – a standard bike is always accepted in the TER and in some TGV, – the trailer is acceptable with the panel vertically, it does not take more space than a bike. For the moment, I have taken the train a dozen times in France and Switzerland, I have never been opposed to refusal.

If necessary, we can reduce the length by sliding the 3rd panel on the 2nd, in less than 10 minutes.

In some trains (TGV and Lyria), we can create the equivalent of a cover with trash bags and big scotch (and for the bike, disassembly of the wheels, and when I have the time, pedals and handlebars before putting it in a bag).

July 21, I finish cycling back to Dijon, at 34 km/h average speed.

Training for the 2019 Sun Trip Tour

In May: first technical test outlets to bring out any weaknesses of design, make improvements that will then be tested in turn (~ 1000 km approximately).
In June: outings to train the cyclist and test the machine on long journeys(~ 2600 km approximately).

Ver en pantalla completa

H : mn

 The battery of my solar bike connected in bluetooth!

It was at the Sun Trip 2019 and 2020 preparation weekend that I discovered this innovation. Thanks to Ralf!
So I decided to replace the BMS of my battery (battery management system) by a model with a bluetooth communication device. It cost me about thirty euros and a little more time than I imagined for the installation. Indeed, the connection pads of the BMS were different and I had to use the soldering iron.

No matter, I am satisfied with the result: now, I can know everything about the status of my battery, in real time, on the dedicated smartphone application. I still added a switch: it allows me to turn off the bluetooth module to avoid unnecessary discharge of the battery, for example during winter storage.

New on the Solarduino Bike: version 3.1 in test!

March 2019 version
Solarduino Bike v3.1
April 2019 version

Apparently nothing has changed between the March version and the April version 3.1. I simply changed the 3 solar panels! I replaced the old economics panels with high quality panels, made of the latest Sunpower ™ Maxeon photovoltaic cells, in the highest “class” or “grade”. Indeed, after manufacture, the cells are sorted into different classes according to their performance (Sunpower ™ uses a particular classification with well over 4 classes).

Result: 86% more solar energy for the same surface! What a difference !

I realize that in 2018 I thought to ride with 200Wc but in fact I had only 107Wc real. To have the same power, only 1 of the new panels would have been necessary, my trailer would have been 2 times shorter, lighter, hyper-manageable. In 2019, I chose to increase the panel area for more power. I wish: – to have more autonomy in case of cloudy weather with clearings, not to be worried about finishing a day “on the pedal”, – to ride faster if necessary, – to ride longer to travel greater distances.

A new type of solar bike on the Sun trip tour 2019!

Previous editions of the Sun trip have seen a wide variety of bikes: Classic straight bikes, tandems, but also recumbent bikes, recumbent tricycles, tandem-lying tricycles, cargo bikes, a seated/reclining tandem and, for a short appearance, a family bike with 4 wheels…
But no mobile bikes had yet participated. This will be the case this year with Bertrand Touzet: on July 6, he will start the Sun trip tour 2019 with his mobile bike whose fairing improves aerodynamics.
Bertrand makes us discover his vehicle in this short video:

The operation of a solar panel, by Christophe Dugué

It was during the course of preparation for Sun trip 2019 and 2020, in Lans-en-Vercors, that Christophe Dugué gave us important information about solar panels. In a very clear presentation, he explained to us the design and operation of a solar panel, the definition of its technical characteristics (maximum power) etc…
Christophe also informed us about practical aspects important for solar cyclists: the influence of temperature on performance, the impact of shading, the consequences of micro-cracks in photovoltaic cells…

The solar panels are its domain: Christophe works at Photowatt, a french manufacturer of solar panels for houses and buildings.
And most importantly, Christophe designed and manufactured prototype solar bike panels. These panels are both light and rigid, therefore resistant to the hazards of a solar bike trip. Christophe tested his first prototype during the Sun trip Tour 2017. Then Stéphane Bertrand was equipped for the Sun trip 2018, Lyon-Canton. For the Sun trip Tour 2019, Christophe will also equip his wife who will participate with him.

Preparation for Sun Trip 2019 and 2020

In mid April, the Sun trip team organized a weekend of preparation for the Sun trip. The aim of this internship was to help the participants better prepare themselves from a technical point of view:

  • understand the operation of solar panels,
  • know the different components of a bike with electric assistance (motor, controller, battery…),
  • share experiences from previous Sun trips,
  • prepare itineraries…

This weekend was intense and very rich, as well by the contributions of the speakers: Florian Bailly (creator of the Sun trip), Christophe Bayard (Association Vécolo), Christophe Dugué (Photowatt), Bernard Cauquil (Professor industrial technical and suntriper 2015 and 2020) and by exchanges between participants.
Thank you all!

Here is a video that translates the atmosphere of these encounters:

Cost of my new solar bike: Solarduino Bike version 3.1

This week, I installed new, very good quality solar panels on my bike. Their real power is 86% higher than that of my old panels. I went from Solarduino Bike 3.0 to version 3.1!

How much did my new 2019 solar bike cost?
I counted the different elements used. I acquired some for the first project in 2017, others in 2018 and 2019. Here is the summary:

The cost of the trailer may seem trivial, the reason is that I mainly used salvage parts (fork and bicycle frames) acquired in the participative workshop La Rustine in Dijon.

Comparative energy efficiency test of 3 flexible solar panels

After several days of rain, the Sun came back! It is slightly veed but no matter: I was too eager to test the solar panels received three days earlier! I compared them to the panels bought in 2017 and 2018. Although this test has no scientific value, the observations have seemed interesting enough to be published.

Test panels

Solar Panel 50W

Solar Panel 50W

Panel A
specified power: 50Wc nominal
number of cells: 4 x 4 = 16
cell manufacturer: unspecified
cell class: not specified
provenance: purchase from a reputable reseller on internet
price: 2 x €142 = €284 for 100Wc in 2017
Panel B
specified power: 100Wc nominal
number of cells: 5 x 6 = 30
cell manufacturer: unspecified
cell class: class C (visible defects)
provenance: purchase on a famous auction website
price: €135 in 2018
Panel C
specified power: 110Wc nominal
number of cells: 5 x 6 = 30
cells: SunPower™ Maxeon
cell class: class A
provenance: purchase from Linksolar manufacturer
price: €350 (~ 395 USD) in 2019

Measuring the instantaneous power of the panels

Not having a solar energy measuring device, it was not possible for me to measure the actual performance of each Panel. So I chose to measure the instantaneous power of the panels with wattmeters, in the sunshine conditions of the moment. And I compared 2 to 2 the panels connected each to an identical charge regulator charging the same battery.

Measured power with panels B and C

Measured power with panels A and C

Reservations about the test protocol

Various elements could impact the outcome of the measures and their analysis:

    • difference in the years of panel manufacturing, in a context of steady progression of cell performance;
    • difference in State of obsolescence and use of panels: Panel C totally new, Panel B having travelled several thousand km (vibrations + shocks), Panel A of 2017 never used and stored;
    • calibration difference of non-certified wattmeters;
    •  measurements made by veted Sun (repeat the test in other conditions of sunshine).

However, these elements can not fundamentally call into question the results obtained.

Calculations and results

The C Panel being the most powerful, I took it as a reference.  I calculated the ratio of the power produced by Panel A or B to the power produced by Panel C. The table above shows the relative efficiency of panels A and B in reference to Panel C, which therefore has an efficiency of 100%. Pushing the reflection further, I imagined an increase in the surface of panels A or B to get the same power as the C Panel. I then calculated the cost in corresponding A or B panels, and the corresponding panel surface.

Comparative table of the yield of 3 solar panels
NB: I took into account the difference in the number of cells (Panel A: 16 cells, panels B and C: 30 cells).
When observing this table, the following remarks can be issued:
Real power

  • panels A and B have almost identical power while panel A is 2 times more expensive than panel B;
  • the power of panel C is almost double that of panels A and B.

Price to get the same real power:

  • at equal power, panel A is 71% more expensive than panel C;
  • at equal power, panel B is 21% cheaper than panel C.

Surface to achieve the same real power:

  • at equal power, panels A and B occupy 90% more surface area than panel C.

Personal notes

Objective and subjective criteria had guided my purchases:

  • in 2017, I totally discovered the universe of the solar panel, it had reassured me to buy at a large recognized website, the many exchanges by phone and email had given me confidence.
  • in 2018, I wanted to experiment with a low-spread panel format (6×5 = 30 cells) and I had found on the market only these panels at low prices.
  • in 2019, I had the urge and the opportunity to invest in quality equipment, to increase the performance of my bike.


  • A high price is not always a guarantee of the performance of the equipment.
  • Lower yield panels (50%) have a strong impact on the solar bike: less autonomy or increased dimensions. In both cases, this will degrade the rider’s comfort and safety.
  • A higher expense for quality equipment ultimately represents an economy: the value for money is much better.
    Not to mention the other benefits: autonomy, maneuverability, performance…